This invention relates generally to a method for coating titanium and titanium base alloys. More particularly, this invention is concerned with providing protection for titanium and titanium alloys against the degradative effects of corrosion under stress conditions.
The recent advent of high altitude and high speed aircraft and missiles has created a need for materials which exhibit high strength and high resistance to oxidative and corrosive degradation at elevated temperatures. The need for such materials becomes even more acute when one considers the great strains and stresses produced in structural elements during operation within a high speed, high altitude environment. Titanium and titanium alloys are well known for their corrosive resistance and find their main application in the aircraft industry, where high strength, coupled with light weight, is a design criteria. These materials, however, do not possess sufficient stress corrosion resistance to meet the demands of present day aircraft and missiles.
In attempting to overcome this problem and provide titanium elements with a high degree of stress corrosion protection without mechanical property degradation, it has been found that immersing a titanium element into an aqueous solution of amonium phosphate followed by the step of heating the element provides a coated element which exhibits improved resistance to stress corrosion cracking.